Foldable multiple section platform assemblies for structural entries such as the rear of trucks are well-known. Their purpose is to decrease the platform area when not in use. Known examples of the type wherein hinge between an inner and outer platform section rises and the outer section folds against the inner section on the outer side are Erlinder U.S. Pat. Nos. 3,831,788, and Perkins 4,007,844. This invention relates to a platform which folds in this pattern.
A disadvantage of this type of platform assembly is that, while the platform is structurally reliable when unfolded and horizontal, its predictability decreases when being folded or unfolded, and when the platform is in its stored condition. In its stored condition the outer platform section, unless properly hooked, can dangle and assume a wide variety of positions. This can constitute a potential risk.
Furthermore, in the transition between the folded and unfolded positions, it has been customary to use chains which do not give positive control and which are subject to slippage. These constitute risks of malfunction.
It is an object of this invention to provide a controlled-folding and controlled-unfolding multiple section platform assembly wherein the angle between the two platform sections is a unique function of the position of the inner platform section by providing fold control means for this purpose.
It is another object of this invention to provide a controlled-folding and controlled-unfolding multiple section platform assembly wherein the angle between the two platform sections is a unique function of the position of the inner platform section by providing fold control means for this purpose.
It is another object of this invention to provide fold control means by eliminating flexible members, using only rigid members which are pivotally joined to one another so as to provide for rigidity of the system at all of its operating positions and for said uniqueness of position of the platform sections relative to one another and to the structure to which it is attached.
It will also be noted that, in prior art devices which utilize flexible chains, if the platform is lowered onto an obstruction such as a curb or a rock it has unlimited tilt and can dump objects which may be on the platform. It is an object of this invention to provide a platform which will have limited tilt relative to its mounting when it is lowered onto an obstruction, and this is due to the general rigidity and positive control of the system.
A platform assembly according to this invention utilizes an inner platform section and an outer platform section which are joined together, the inner platform section being hingeable to structure associated with a structural entry. Fold control means comprises a pair of rigid support members which are hinged together, and a rigid co-ordinating member which extends between the inner platform section and the outermost one of the rigid support member. As a consequence of the correct proportioning of the element of this device, when the inner platform section is tilted the outer platform section will assume a unique angular position relative to it for each one of the angular positions of the inner platform sections.
According to a preferred but optional feature of the invention, the platform assembly includes a substantially vertical track, and a carriage restrained to the track for movement along the track whereby the platform sections can be raised and lowered.
According to still another preferred but optional feature of the invention, angle control means is selectively engageable and disengageable to the structure and is engaged to the inner platform section whereby selectively to tilt the inner platform section when it is desired to fold the platform assembly.